1. Field of the Invention
The present invention relates generally to an ignition system for an internal combustion engine, and more specifically to an ignition system for an internal combustion engine, wherein an ignition coil and spark plug are integrally incorporated into each engine cylinder to eliminate ignition energy loss caused by conventional high-tension cables and a DC-DC converter for boosting DC voltage is connected to the secondary winding of each ignition coil so as to operatively apply a high DC voltage across each spark plug so as to extend the discharge duration of each spark plug under such an engine operating condition as a low engine speed (engine start, idling speed, etc.) and light engine load conditions.
2. Description of the Prior Art
A conventional ignition system for an internal combustion engine includes:
(a) a low DC voltage bias supply such as a vehicle battery;
(b) an ignition signal detector biased from the low DC voltage bias supply for detecting and outputting an ignition reference signal;
(c) an ignitor for intermittently firing spark plugs;
(d) an ignition coil connected to the ignitor at the primary winding thereof and to the DC bias supply at a center tap of the primary winding; and
(e) a plurality of diodes, each connected between a corresponding plug and either end of the secondary winding of the ignition coil so as to form a current circuit with other plug(s) at an opposite end of the secondary winding. The ignitor comprises: (a) an spark advance angle controller connected to the ignition signal detector for controlling the spark timing of the spark plugs related to the ignition reference signal; (b) a pair of primary current controllers connected to the spark advance angle controller; and (c) a pair of power transistors, the base of each being connected to the corresponding primary current controller, the emitter of each being grounded, and the collector of each being connected to the corresponding end of the primary winding of the ignition coil. Each primary current controller controls the turning-on interval and timing of the corresponding power transistor according to the output signals from the advance angle controller so that the primary winding of the ignition coil provides a current flow of opposite directions.
In such a conventional system of the construction described above, the primary winding of the ignition coil provides an alternating current flow so that the secondary winding thereof produces a multiplied high AC voltage. The AC voltage generates the spark discharge twice within one engine cycle at each spark plug, i.e., first in the compression stroke and second in the exhaust stroke. The ignition system described hereinabove is a "Haltig" ignition system. In such ignition system, there is an advantage that the efficiency of ignition energy is enhanced with the elimination of transmission energy loss, since there is no conventional mechanical distributor and central cord associated with the distributor.
However, since the conventional ignition system ignites twice during each engine cycle for each engine cylinder, it loses the effect of eliminating the mechanical distributor and avoiding large power consumption from the vehicle battery as the low DC bias supply and wasteful fuel consumption accordingly results. The weight of the ignition coil is increased so that a wider space is required. Furthermore, it is difficult to improve the combustion performance by increasing or decreasing the ignition energy according to various engine operating condition since the polarity of electrodes of the spark plugs is continuously reversed.